1. Field of the Invention
The present invention relates to a rotary sensor, for example, a throttle position sensor mounted in a vehicle and used for the purpose of detecting the position of the throttle valve according to the amount of pushing the gas pedal and, in particular, to a rotation shaft bearing structure which prevents the sensor rotation shaft from becoming eccentric.
2. Description of the Related Art
FIGS. 30 and 31 illustrate a conventional rotary sensor of this type. The conventional rotary sensor comprises a cup-shaped housing 31 formed of synthetic resin. An annular wall portion 31 is integrally formed with a cylindrical external connection portion 33, and three lead-through terminals 34 (only one of which is shown) are mounted by insert molding. The interior of the annular wall 32 constitutes an accommodating portion 35, the end portions of the three lead-through terminals 34 being arranged in the accommodating portion 35 and the external connection portion 33.
In the bottom wall portion 36 of the housing 31, a metal bearing 37 is mounted by insert molding, and a plate-like rotating member accommodated in the accommodating portion 35 and formed of an insulating resin has a rotation shaft 38a rotatably supported by the bearing 37, forked sliders 39 formed of a conductive material being supported by the rotating member 38. And, to the forward end portion of the rotation shaft 38a, there is firmly attached a lever member 40 outside the housing 31, and due to this lever member 40, the rotation shaft 38a is prevented from being detached.
Further, on the inner peripheral surface of the annular wall portion 32 of the housing 31, there is formed a step portion 32a, and a circuit board 41 formed of synthetic resin or ceramic abuts this step portion so as to be fixed in the accommodating portion 35 such that it is opposed to the rotating member 38. And, on the surface of the circuit board 41, there are formed by printing a resistor pattern 42 which is arcuate around the rotation shaft 38a and a collector pattern 43, and the sliders 39 are in contact with them to establish electrical connection between the resistor pattern 42 and the collector pattern 43. Further, eyelet-like terminals 44 (only one of which is shown) are fixed to the circuit board 41 at both ends of the resistor pattern 42 and one end of the collector pattern 43, and one end of each of the three lead-through terminal 34 is soldered to the forward end portion of each of them.
Further, in the bottom wall portion 36 of the housing 31, there is formed on the opposite side of the accommodating portion 35 a recess 45 so as to be opposed to the lever member 40, and a coil spring 46 is accommodated in the recess 45 such that a part of the bearing 37 is accommodated in the winding portion thereof, the free ends 46a and 46b of the coil spring 46 being engaged with the recess 45 and the lever member 40.
Further, a cover 47 formed of synthetic resin is fitted into the opening 35a of the housing 31 on the back side of the circuit board 41, and this cover 47 is supported by the housing 31 by crushing the periphery of the opening 35a of the housing 31 by heat caulking, thereby enclosing the interior of the accommodating portion 35.
In the rotary sensor, constructed as described above, the lever member 40 is connected through a drive pin 49a to a rotary disc 49 fastened to a drive shaft 48, which rotates by a predetermined angle in accordance with the position or opening angle of the throttle valve of an internal combustion engine (not shown), a predetermined voltage being applied to both ends of the resistor pattern 42 through a connector (not shown) fitted into the external connection portion 33, the lead-through terminals 34 and the terminals 44.
And, when the rotation of the drive shaft 48 is transmitted to the lever member 40 through the rotary disc 49 and the drive pin 49a, the rotation shaft 38a and the rotating member 38 rotate integrally with the lever member 40, and, with that, the sliders 39 slide on the resistor pattern 42 and the collector pattern 43. As a result, a voltage according to the position or opening angle of the throttle valve is generated in the terminal 44 fastened to one end portion of the collector pattern 43. This voltage is output to the exterior of the sensor through the connector, and used as a throttle valve position signal for controlling an internal combustion engine or the like.
As shown in FIG. 31, in the above-described conventional rotary sensor, a little clearance t is provided between the rotation shaft 38a and the inner peripheral surface of the bearing 37 so that the rotation shaft 38 can rotate. Thus, when the rotation shaft 38a rotates in a condition in which it s radially eccentric (in the directions of the arrows A), the rotation of the rotating member 38 as a result of the rotation of the rotation shaft 38a causes the rotating member 38 to rotate in an eccentric state, so that the sliders 39 are deviated from the regular circular paths. As a result, the linearity characteristics of the throttle posit on signal (linear change in the output voltage according to the rotation of the lever member 40) deteriorate. Further, hysteresis is generated in the throttle valve position signal, making it impossible to correctly detect the position or opening angle of the throttle valve.
The present invention has been made in view of the above problem in the prior art. Accordingly, it is an object of the present invention to provide a highly reliable rotary sensor in which radial eccentricity of the rotation shaft is prevented, making it possible to perform correct detection.
To achieve the above object, there is provided, in accordance with the present invention, a rotary sensor comprising a rotating member having a rotation shaft, rotation detecting means for detecting the rotation of the rotating member, a bearing having a shaft hole into which the rotation shaft is inserted and which rotatably supports the rotation shaft integrally with the rotating member, and biasing means for imparting a biasing force in a thrust direction to the rotation shaft, wherein there is formed in the periphery of one end portion of the shaft hole a beveled portion inclined so as to be outwardly flared in the radial direction of the shaft hole, and wherein the rotating member is provided with a tapered surface corresponding to the beveled portion, the tapered surface being held in press contact with the beveled portion by the biasing force.
In the above construction, there are provided a housing having an accommodating portion accommodating the rotation detecting means and a lever member adapted to rotate integrally with the rotation shaft, the bearing being provided in the bottom wall portion of the housing, the accommodating portion communicating with the exterior of the housing by the bearing, the lever member being arranged on the opposite side of the accommodating portion, the bottom wall portion having a recess accommodating the biasing means on the opposite side of the accommodating portion, the biasing means biasing the rotation shaft through the lever member.
Further, in the above construction, the rotating member is accommodated in the accommodating portion, and wherein, in the radial direction of the hole portion, on the outside of the beveled portion of the bearing and the tapered surface of the rotating member, the biasing member biases the lever member such that it is separated from the accommodating portion, thereby bringing the beveled portion into press contact with the tapered surface in the accommodating portion.
Further, in the above construction, the biasing means is formed by a single coil spring, the bearing being accommodated in the winding portion of the coil spring.
Further, in the above construction, the free ends of the coil spring are engaged with the recess and the lever member, the lever member being automatically restored to the initial position with the rotating member by the elastic force of the coil spring.